Method for dewaxing hydrocarbon oils



METHOD v.FOR DEWAXING HYDROGARBON' oILs Filed Jung-29, 1954 "4isheetsfshe'et 2 INVENTORS. DBBANKS AND F! D. BARTON.

ATTORNEYS.

oct. 27, "1936. D.' B. BANKS TAL- 2,059,166 1 METHODFOR DEWAXING. HYDROCARBON OILS Filed June 29, 11934 4 shee'S-sh'eet 4 j WASH I F/L TER Patented Oct. 27, 1936 UNITED STATES METHOD FOR DEWXISNG HYDROCARBON 1L Daniel B. Banks, Upper Darby, Pa., and Paul D. Barton, Scarsdale, N. Y., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application June 29, 1934, Serial No. 733,022

6 Claims.

The present invent1on relates to the dewaxing of hydrocarbon oils and more particularly to a method and apparatus for separating finely divided crystalline and amorphous wax from the oil.

It has been found that in certain types of wax bearing distillates, particularly the lighter fractions, or oils in which light fractions predominate, that by normal chilling fractional crystallization takes place. This -is typical of a long residue stock or a long distillate which carries the entire or combined waxes of the crude. These waxes are normally segregated into fractions so that the lighter fraction will carry the crystalline waxes which are pressable, and the heavier fractions of more viscous oil waxes which are centrifuged. v

When theentire lube oil portion of the crude is segregated and blended with a diluent and chilled, it will be found that fractional crystallization takes place to the extent that so much of the crystalline type waxes are precipitated that the entire solution becomes a thick slurry due to the interlocking effect of the crystalline wax on the entire mass. This increased viscosity makes it diicult to crystallize the more amorphous waxes.

This can be done by two methods; first, by two stage dewaxing, i. e. removing the crystalline wax at a proper predetermined temperature either by treating and removing with sludge, or by filtering. This will make it possible to precipitate the balance of the wax, i. e. the amorphous type, at temperatures of, say -45 to 50 F. The second method is to chill the entire mixturetoa very low'temperature, say `65 F. and then lter the entire mass under' pressure.

It has been found that either method will give the same results as to cold test and wax removal.

The ordinary pressure system of filtration depends for its operation on the establishment of pressure on the liquid at the upstream side of the filter. This pressure may be considerably above the vaporization equilibrium pressure of the mixture to be ltered at Vthe temperature which exists at the upstream side. When such practice is followed it will be observed that there will be formed on the filter leaves a series of layers of solidified wax-like compounds. The operation of the iilters in such a pressure system is accompanied by a continuous flow of heat from the exterior of the units to the oil-wax solvent contained therein. This is normally substantially overcome by counterflow of cold material derived from the mixture being filtered, AS the wax cake builds up on the filter leaves, there is a gradual decrease in the rate of flow of theltrate which is utilized for cooling until the amount is insufficient to absorb the characteristic amount of heat flowing in continuously from the exterior. During the refrigeration of the oil solvent solution, each stage of temperature reduction will result in a new series of wax-like compounds being crystallized. Similarly, during the filtration, as the temperature of the wax cake increases due to inadequate cooling, there will be a progressive re-dissolving of the lower melting series of waxlike compounds in the wax cake bythe filtrate. The result will be a gradual raising of the cold test of the filtrate as well as a gradual softening of the lower melting point series of wax compounds accumulated on the filter leaves. This softening will ultimately tend to render the cake substantially impervious, thus blocking the flow of wax free oil through the lters. In such a case early shuttingdown of the lter unit for cleaning of the leaves is necessitated before operation can be resumed, resulting in loss of time, uneconomical operation, and general lack of feasibility from a commercial standpoint. An improved method of carrying out the low temperature method has been found by combining the temperature reduction, the solidification of the lower melting waxes, and the filtration into one operation. Such a method is disclosed in our copending application Serial No. 720,730, filed April 16, 1934. 1

It is the object of this invention to provide a method and apparatus for continuously separating crystalline and amorphous wax from a mother solution containing substantial 'amounts of a normally gaseous hydrocarbon.

It is a further object to provide a method and apparatus for continuously removing from the lter meanswax which is separated from the mother solution.

In the accompanying drawings which form a part of this specification, and are to be used in conjunction therewith, and in which like numbers refer to like parts throughout the several views:

Fig. 1 is a schematic showing of an apparatus embodying this invention and capable of carrying out the process of this invention.

Fig. 2 is an end view in elevation of the filter embodying this invention.

Fig. 3 is a longitudinal section, partly in elevation, of the filter taken on line A-A of Fig. 2.

Fig. 4 is a transverse section of the lter taken on line B-B of Fig. 3.

Fig. 5 is a detail View showing means for attaching the filter cloth to a lter drum.

Figs. 6 and 7 are detail sectional views showing the means for attaching the lter cloths to the lter drum.

Fig. 8 is a detail section taken on the line C-C of Fig. 3.

Fig. 9 is a detail section taken on the line D-D of Fig. 3.

The apparatus embodied in this invention comprises pipe I for conveying chilled mixture of propane, oil and wax to a tank indicated at E in Fig. 1. The tank is connected by means of discharge pipe 2, valve 3, and pipe 4, to filter indicated at F. The tank E also has a vent pipe 5 connected by pipe 1 (containing valve 6) leading to propane recovery and supply system not shown. Pipe 8 leads from vent pipe 5 through valve 9 and pipe I0 to the filter F. Arranged within the filter element is a lter drum l I which is connected by pipe I2 With a suitable separator |29, which connects, through pipe I 2| with a vacuum pump (not shown) and, through pipe |22, with storage. A wax discharge chute I3 leads from filter F to wax depropanizing tank G. Arranged within the bottom of tank G is a steam coil I5 to Which steam is supplied through pipe I6 and Valve I1 from any suitable source. Any steam condensate formed in the coil I5 is discharged through pipe I8. A propane outlet pipe I9 leads from the tank G through valve 2G and pipe 2| to pipe 1 connected to the propane recovery system. A wax discharge pipe 22 leads from tank G through valve 23 and pipe 24 to a suitable wax storage tank not shown.

The lter embodied in this invention, shown more in detail in Figs. 2., 3, and 4, comprises a casing 25, mounted on any suitable supports 26. A suitable cover 21, is bolted to the casing 25. Arranged in the top of the cover is a safety valve 28. Positioned within the filter casing 25 is a drum I I supported at one end by means of radial tubes |4 affixed to a collar Welded to shaft 33, and supported at the other end by radial conduits 46 which are affixed to a hub 49, also welded to shaft 30. Shaft 38 at one end is journaled in packed bearing 3| having a packing retainer 52 holding the packing 32. At the other end the hub 49 is journaled in a similar bearing 32 having packing 53 and packing retainer 5|. The shaft 30, and consequently the drum II, is rotated by any suitable driving means which may be associated with sprocket 33 at the end of shaft 38.

At each end of drum there is welded a ange 69 having an undercut slot 10 therein, and positioned at spaced intervals around 'the drum II there are separators 34 having undercut slots 1| therein. These separators extend axially of the drum and form with the flanges 69 and the filtering medium, hereafter described, a plurality of separate chambers. Welded to each edge of each of the separators 34 and the internal edges of the flange 69 are perforated plates 36 and superposed wire screens 39. A lter cloth 38 is stretched across each of the screens 39 and is drawn and held taut by means of cords 'I2 forced into the undercut grooves in separators 34 and anges 69. This construction is clearly shown in Figs. 5, 6, and 7. Arranged over the tightened iilter cloths 38 are cover strips 39 held in place on separators 34 by means of screens 4i). At one side of the lter drum is a scraper 4I mounted on shaft 42 held against the lter cloth 38 by a spring 43.

Arranged within the topof the filter casing 25 are propane spray pipes 44 connected through pipe 45 to the source of propane supply. At one end of the lter drum, as shown more particularly in Figs. 3 and 4 are conduits 46 leading from the spaces 41 between the filter drum I and filter surface 35 to the corresponding conduits 48 in the hub 49 mounted on shaft 30, and welded thereto as at 50.

Loosely mounted on the shaft 30 adjoining element 49 is a plate 54 having lugs 16, and having an annular slot 55 therethrough which extends through an arc of approximately 225. Slot 55 registers with some of the conduits 48 in hub 49, depending upon the position of the hub. This plate is held in split ring 56 having clamping bolt 15 and having a handle 51 for rotating the plate 54. Plate 54 is normally clamped. to manifold 6D described hereinafter. A pipe 58 connected to a suitable source of gas under pressure not shown, is connected with an opening 59 in the plate 54 adapted to register with one of the conduits 48 in hub 49. A manifold 68, having an annular opening 6| therein, extending through an arc of 270 and adapted to register with slot 55 in plate 54 loosely mounted on shaft 3) adjoining plate 54. This element 6D is resiliently supported from the casing 25 of the filter and held against rotation by a spring supported Y member 62 in turn supported by bracket 13, bolted to the casing. The vacuum line I2 is attached to the element G8 and is connected to opening 5| therein. A spring 14 retained inlthe end of shaft 38 by a nut B3, presses manifold 60 tightly against plate 54, and plate 54 tightly against 49.

A suitable opening 64 having a removable cover 65 bolted in place is provided in the casing 25 opposite the scraper 4| to permit repairs and adjustment being made to the scraper.

A drain or clean-out opening 51 closed by cap 63 is provided in casing 25 for cleaning the filter casing.

The method of operation of this apparatus is as follows:

The chilled solution of propane, oil, and Wax is introduced through pipe I into tank E. This solution at about 45 to 48 F. Will be at substantially temperature and pressure vaporization equilibrium conditions, that is no vaporization of propane will occur at the existing temperature *45 to 48 F.) and the existing pressure (atmospheric). This temperature and pressure vaporization equilibrium will be maintained, in tank E, by venting propane gas, which may form due to ineffective insulation, either through valve 9 and pipe 1 to the propane recovery apparatus or through pipe 8, valve 9, and pipe I0 to the filter. While in the tank the oil as already described is maintained at approximately 45 F. and at that temperature wax from the oil will be in suspension in the oil-propane solution. This mixture from tank E passes through pipe 2, valve 3, and pipe 4 to the lter F, entering the lter through the bottom of casing 24. The mixture of propane, oil, and Wax is maintained at approximately the level shown in Fig. 1, so that substantially one-half the filter surface is immersed in the mixture. Suction is applied to the filtering drum II through vacuum line I2. This suction draws the oil and propane through the totally immersed filtering surfaces 35 into the spaces 41 between the filtering surfaces 35 and the filter drums. rThe mixture of oil and propane passes from each immersed space 41 through the radial conduits 46 into the axial conduits 48 in hub 49. The plate 54 is so adjusted that that portion of the opening therein below the horizontal center line of Fig. 8 registers with the conduits 48 connected to the spaces 4'! then immersed in the liquid. The oil in the conduits 48 passes through the plate 54 and into the opening 6| in manifold 60, thence through Vacuum line l2 to the vacuum chamber and any desired weathering apparatus. The drum is slowly but continuously rotated, at approximately one revolution every 4-6 minutes, and as the oil-propane solution passes through the filtering surface 35, the wax in the solution collects on the filtering surface in the form of a lter cake.

Due to the reduction in pressure through the filter surface 35 by the vacuum maintained in the spaces 41, the temperature-pressure equilibrium of the oil-propane solution will be disturbed and some of the propane in the mixture being filtered will vaporize, thus lowering the temperature and re-establishing equilibrium conditions. This vapor passing through the filter cake along with the oil and the propane will tend to keep the filter cake pervious. Also the drop in temperature through the filter vcake (approximately 15 F. if the vacuum is about 10 inches of mercury) caused by the vaporization of part of the propane, will separate more wax from the oil-propane solution and retain it With the wax already separated. As the drum is continuously rotated the filter surfaces pass out of the solution of oil, wax and propane and into a washing zone. In this zone liquid propane is sprayed on the filter cake through pipes 44. The conduits 48 in element 49 which are connected to the spaces 41 in this washing zone are also in register with that portion of the opening in plate 54, above the horizontal ccnterline of Fig. 8, so that vacuimi is maintained in the spaces 41 while the filtering surfaces pass through the washing Zone. By this means the liquid propane which is sprayed on the filter cake in this Zone is partly drawn through the filter and partly vaporized taking with it any oil which is retained by the lter cake. Due to the drop in pressure through the filter cake, some of this propane is Vaporized as already stated and maintains the filter cake in a solid condition and also maintains it pervious. As the filtering surface nears the scraper 4| the openings in. the conduits 48 in hub 49, connected to the chambers 41 which are near the scraper pass out of register with the opening 55 Vin plate 54 and come into register with opening 59 in plate 54. An inert gas under pressure is admitted through this opening 59, passes through conduits 48 and 45 to spaces 41 from whence it passes through the filtering surface and the filter cake, loosening the filter cake.

It is to be noted that slot o5 subtends an arc of 225 and that opening 6| in manifold 5|) subtends an arc of 270. By loosening the clamping nut 15 it is therefore possible to move plate 54 by means of handle 51 to change the timing of the blowing through line 5B and suction through line I2. Thus, if the level of liquid in case falls, the handle 51 is rotated in a clockwise direction (Fig. 9) so that the blowing occurs at a later period and so that the chambers 41 do not become connected with suction line I2 until chamber entering the liquid in case 25 is entirely submerged.

The filtering surfaces then pass under scraper 4| and the iilter cake which comprises wax and propane is scraped oif. As the drum continues its rotation, the filtering surface again enters the mixture of propane, oil and wax, and the opening 48 in element 49 connected to the spaces 41 entering the solution come into register with opening 55 in plate 54vand suction is again applied to these spaces 41.

The wax which is scraped off by scraper 4| falls down chute 3 into the wax depropanizing tank G. The wax in this tank is heated and melted by the steam coil |5 in the bottom of the tank, any propane in the wax being vaporized and discharged through pipe I9, valve 20, pipe 3| to pipe 1, leading to the propane recovery apparatus. The depropanized liquid wax is discharged from the tank G through line 22, valve 23, line 24 to a wax storage tank.

From the foregoing it is apparent that an apparatus and process have been provided with which a chilled oil-propane solution containing wax in suspension may be continuously iiltered to remove the wax, the wax washed to remove occluded oil and. depropanized while the filtered oil-propane solution is passed continuously from the system for depro-panizing or weathering.

As a specific example, a Wax bearing distillate containing 16.3% of wax and having the following characteristics: a pour point of +l05 F.; an A. P. I. gravity of 25.5; a viscosity of 118 at 130 F.; and a viscosity of 47.4% at 210 F., was mixed with liquid propane and chilled to 47 F., at which temperature substantially all of the wax in the solution separated out as nely divided crystals suspended in the solution of oil and propane. This chilled mixture consisting of approximately 4.78 parts of propane to 1 part of the wax distillate was continuously charged to the tank E. Th-e pressure in the tank E was maintained at atmospheric pressure by venting any propane gas formed through line 8, valve 9 and line 19 to the filter casing 25, and the chilled propane-oil wax mixture was permitted to continuously flow into the filter casing 25, wherein the mixture was filtered as described above, a vacuum of 10 inches of mercury being maintained on the eduction side of the filter surface 35. The oil-propane solution was continuously drawn through the filter surface and discharged through line l2 to receiver |29, and the suspended wax collected on the iilter surface in the form of a filter cake. The filter cake was washed with liquid propane and removed from the lter surface and discharged through chute i3 to wax depropanizing tank G. The iilter cake discharged through chute i3 was found to consist of 0.163 part of wax, 0.148 part of cil, and 2.895 parts of propane. The filtrate in line I2 had a temperature of 59 F., and consisted of 0.689 part of wax free oil, and 6.414 parts of propane. ltrate was depropanized and the wax-free oil obtained therefrom was found to have the following characteristics: a pour point of 5 F.; an A. P. I. gravity of 22.3; a viscosity of 410 at 100 F.; a viscosity of 52.2 at 210 F.; anda viscosity index of 42. Any propane gas formed in the filter casing 25 `due to ineffective insulation, or introduced thereto by venting gas from tank E, was vented through chute I3 to wax depropanizer tank G. The gas thus introduced into tank G and the propane gas driven from the wax therein was discharged through pipe I9, valve 20, and pipe 2| to pipe 1 leading to the propane recovery apparatus.

Where in the appended claims equilibrium conditions are referred to, the term is to be construed to cover that state in which the liquid, whether propane-oil solution or propane, if maintained at the same temperature, will not generate a higher or lower vapor pressure and if main- TheI tained under the same pressure Will not rise or fall in temperature.

While in the specification and appended claims propane has been specifically referred to, it is meant to include other liquefied normally gaseous hydrocarbons or mixtures of them as equivalents.

Having now described our invention, what We claim and desire to protect by Letters Patent is:

l. A continuous process for filtering suspended Wax from a chilled solution of oil and a normally gaseous hydrocarbon such as propane, which comprises conveying a filtering medium along a zone containing such chilled solution at substantially vaporization equilibrium pressure for the existing temperature, maintaining a reduced pressure on the eduction side of the ltering medium to cause the solution to penetrate the same and the wax to collect on its induction surface, substantially continuously replenishing the chilled solution from a feeding zone and progressively removing the wax cake after progressive areas oi' the same are carried by the traveling filter medium beyond the Zone of wax deposition, whereby partial vaporization of the propane, by liberation of vapors in the filtering medium, maintains the wax cake pervious and, While disturbing equilibrium conditions, lowers the temperature and reestablishes equilibrium conditions in th-e filtrate, and whereby the travel of the filtering medium as aforesaid effects the deposition of a predetermined layer of Wax without interruption of its continued deposition.

2. A continuous process for filtering suspended Wax from a chilled solution of oil and a normally gaseous hydrocarbon such as propane, which comprises conveying a filtering medium along a zone containing such chilled solution at substantially vaporization equilibrium pressure for the existing temperature, maintaining a reduced pressure on the eduction side of the filtering medium to cause the solution to penetrate the same and wax to collect on its induction surface; passing the filtering medium with the Wax thereon along a Washing Zone wherein it is contacted with i, a chilled liquid normally gaseous hydrocarbon,

zone containing such chilled solution at substantially vaporization equilibrium pressure for the existing temperature, maintaining a reduced pressure on the eduction side of the filtering medium to cause the solution to penetrate the same and wax to collect on its induction surface; passing the filter medium with the Wax thereon along a Washing zone wherein the induction side of the filtering medium is contacted With other quantities of said chilled liquid normally gaseous hydrocarbon, maintaining on the eduction side of the washing Zone such reduced pressure for the existing temperature as to cause said hydrocarbon to penetrate the Wax and be partly Vaporized and take with it oil that has been retained by the Wax and maintain the Wax pervious; passing the filtering medium with the Wax thereon tlnough another zone and blowing gas therethrough in a direction the reverse of the fluid iiow in the Wax-deposition and Washing zones and thereby loosen the iilter cake; and then removing the wax from the filtering medium.

Il. A continuous process for filtering suspended Wax from a chilled solution of oil and a normally gaseous hydrocarbon such as propane, which comprises establishing in a feeding Zone a body of such chilled solution at substantially Vaporization equilibrium pressure for the existing temperature, passing said solution to a lter zone, conveying a filtering medium along said zone, maintaining a reduced pressure on the eduction side of the filtering medium to cause the solution to penetrate the same and the Wax to collect on its induction surface; passing the filter cake out of the filter zone and Washing it with a chilled liquid normally gaseous hydrocarbon, removing the Wax from the filtering medium and conveying it to a depropanizing Zone, depropanizing the Wax and venting the feeding Zone to the filter zone and the Wax depropanizing Zone.

5. The process set forth in claim 1 in which the reduced pressure on the eduction side of the filtering medium is a sub-atmospheric pressure, thereby avoiding the necessity of providing means to maintain a positive pressure on the induction side thereof.

6. The process set forth in claim 2 in which the reduced pressure on the eduction Side of the filtering medium in both the filtering zone and the washing zone is sub-atmospheric while the pressure on the induction side in both Zones is approximately atmospheric.

DANIEL B. BANKS. PAUL D. BARTON. 

